A post-processing apparatus that performs post-processing, such as binding by a stapler on sheets discharged from an image forming apparatus, is known. For example, the post-processing apparatus stacks sheets on a processing tray, corrects displacement of the sheets in a lateral direction and a longitudinal direction, staples the sheets with a stapler, or the like, and then discharges the stapled sheet bundle to a stacking tray. In the post-processing apparatus, for example, a user may take out the sheet bundle while the sheet bundle is in the middle of being discharged to the stacking tray. In such a case, in the post-processing apparatus of the related art, when the user takes out the sheet bundle, if the sheet bundle comes in contact with a sensor, it is mistakenly determined that the sheet bundle is jammed, thereby resulting in an error.